1. Field of the Invention
This invention relates to an audience rating measuring system for a television and a video tape recorder.
2. Description of the Prior Art
A measuring system called a "Video Meter" has been used in the past to measure the audience rating of television. The Video Meter stores the ON/OFF times of a television receiver, the channel of the program viewed and other data on paper tape or in other memory devices.
As home use video tape recorders have become extremely popular in recent years, however, the conventional audience rating measuring systems cannot cope with the situation. For as long as the television receivers are used alone, the audience state can be accurately determined from audience data such as the ON/OFF status of the television receivers and the channel number because the program is being viewed as it is broadcast. If the television receiver is used in combination with a video tape recorder, however, the viewer does not always view the program on a real time basis but may perhaps record the program and play it back later.
Accordingly, conventional audience measuring systems such as the Video Meter described above have the drawback that although they can record data on programs that are actually viewed when they are received, they cannot provide any data on the use of a video tape recorder.
In the conventional measuring systems of the kind described above, the following method has been used as one of the techniques for detecting the reception channel of the television. Namely, a signal is taken from a sound intermediate frequency circuit inside the television receiver and is compared with a sound intermediate frequency signal obtained from another tuner disposed in the measuring system. The reception channel of the television receiver is determined by sequentially changing the tuning positions of the other tuner until a position is reached where both signals coincide with each other. When a video tape recorder is used in conjunction with the television receiver, however, channel determination as described above cannot be made in the case where the television tuner is set to an unassigned channel allotted to the radio frequency output signal of the video tape recorder in order to view the program by a re-modulated radio frequency signal. This problem is even more difficult when a dial type channel television receiver is combined with a touch type channel video tape recorder because a desired station can be tuned more easily by the touch channel type. In preparation for making a video recording, the channel of the video tape recorder is set to allow monitoring the program through the television receiver.
The problem here is that since the radio wave received by the television receiver is re-modulated inside the video tape recorder, it is different from the sound carrier frequency actually broadcast by the station as is the frequency of the sound intermediate frequency signal. Namely, a radio frequency signal applied to the television receiver from the video tape recorder in order to monitor the program is a re-modulated wave made from an carrier generated in a oscillator disposed in the video tape recorder. Accordingly, it becomes impossible to determine whether the sound intermediate frequency signals are coincident or not by comparing them with each other. Thus, the reception channel of a television cannot be reliably determined.